1. Field of the Invention
The present invention relates to Doppler VOR systems generally, and more particularly to a VOR system in which upper and lower sideband signals are relative phase monitored.
2. Description of the Prior Art
A Doppler VOR system of the type to which the invention applies to disclosed in German Patent No. 2505723. That patent specification shows what measures have to be taken to permit correct monitoring of the radiated signal even in the near field.
Basically, a Doppler VOR transmits carrier and sideband signals. The frequencies of the sideband signals differ from the frequency of the carrier signal by .+-.9960 H.sub.z. Correct transmission requires that the phase of the carrier signal be symmetrical with respect to the phases of the sideband signals.
In the prior art, various approaches have been employed for ensuring the sideband-to-carrier phase relationship but these have usually depended on separate monitoring antennas and other complications.